Work in progress has the dual objective of (a) obtaining higher yields of cell-free varicella-zoster virus (VZV) on propagation in vitro; and (b) adaptation of VZV to a non-primate system. Reports by others of propagation of VZV in a guinea pig cell culture system have been confirmed. Attempts to establish virus grown in this system in newborn guinea pigs are underway. No promising results have been obtained to date on propagation of VZV in genetically defective human cell lines, nor in a single attempt with a mouse-human hybrid cell line.